Specifications

Linking Resistance

Measurements

To link channels to the resistance EU conversion send the

[SENSe:]FUNCtion:RESistance <excite_current>,[<range>,](@<ch_list>)

command.

Resistance measurements assume that there is at least one Current Source SCP

installed (eight current sources per SCP). See Figure 3-6.

The <excite_current> parameter is used only to tell the EU conversion

what the Current Source SCP channel is now set to. <excite_current> is

specified in amps dc and the choices for the VT1505A SCP are 30e-6 (or

MIN) and 488e-6 (or MAX). Select 488 µA for measuring resistances of

less than 8,000 W. Select 30 µA for resistances of 8,000 W and above.

The optional <range> parameter can be used to choose a fixed A/D range.

When not specified (defaulted), the module uses auto-range.

The <ch_list> parameter specifies which channel(s) to link to the resistance

EU conversion. These channels will sense the voltage across the unknown

resistance. Each can be a Current Source SCP channel (a two-wire

resistance measurement) or a sense channel separate from the Current

Source SCP channel (a four-wire resistance measurement). See figure 3-6

for diagrams of these measurement connections.

To set channels 0 through 3 to measure resistances greater than 8,000 ohms and set

channels 4 through 7 to measure resistances less than 8k (in this case paired to

current source SCP channels 32 through 39):

Programming the VT1419A Multifunction

Plus

Setting Up Analog Input and Output Channels

60 Chapter 3

Two-Wire Measurement

(not recommended**)

Four-Wire Measurement

Current Source SCP

Any Sense SCP

Field Wiring

*150 Ohm 5%

* Because of the 150 Ohm resistor in series with each of the

current source outputs, Two-Wire resistance and temperature

measurements will have a 300 Ohm offset.

** The current source HI terminal is the negative voltage node.

The current source LO terminal is the positive voltage node.

Figure 3-6: Resistance Measurement Sensing

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